Jet engine nozzle system for noise suppression

ABSTRACT

A plurality of secondary nozzles or tubes and a plurality of shrouds, each coupled to the outlet of a respective tube, are aligned with the axis of a primary nozzle and coupled thereto to provide a nozzle system of short axial length in which noise emission is substantially reduced over what would be emitted by the exhaust from the primary nozzle in the absence of such tubes and shrouds.

United States Patent Inventors Henry T. Nagamatsu Schenectady;

Russell E. Sheer, Jr., Cohoes, both of N.Y. 857,260

July 31, 1969 Dec. 28, 1971 General Electric Company Appl. No. Filed Patented Assignee JET ENGINE NOZZLE SYSTEM FOR NOISE SUPPRESSION 3 Claims, 2 Drawing Figs.

US. Cl 181/33 HC, 181/51,181/56,181/60, 239/l27.3, 239/265.17 Int. Cl F0ln l/l4, B64d 33/06 Field of Search 181/33, 33.22, 33.221, 43, 51, 46, 56, 60; 239/1273, 265.17

[56] References Cited UNITED STATES PATENTS 2,075,316 3/1937 Tyden 181/46 2,633,703 4/1953 Tenney et a]. 181/33 (.22) 2,995,200 8/1961 Seifert 181/60 X 3,139,153 6/1964 De Remer 181/43 3,447,630 6/ 1969 Davidson 181/60 Primary Examiner-Robert S. Ward, Jr.

AnorneysPaul A. Frank, John F. Ahern, Julius .l.

Zaskalicky, Frank L. Neuha-user, Oscar B. Waddell and Joseph B. Forman ABSTRACT: A plurality of secondary nozzles or tubes and a plurality of shrouds, each coupled to the outlet of a respective tube, are aligned with the axis of a primary nozzle and coupled thereto to provide a nozzle system of short axial length in which noise emission is substantially reduced over what would be emitted by the exhaust from the primary nozzle in the absence of such tubes and shrouds.

JET ENGINE NOZZLE SYSTEM FOR NOISE SUPPRESSION The invention described and claimed in the US. patent application herein resulted from work done under United States Government contract FA-SS-677. The United States Government has an irrevocable nonexclusive license under said application to practice and have practiced the invention claimed herein including the unlimited right to sublicense others to practice and have practiced the claimed invention for any purpose whatsoever.

The present invention relates to the suppression of noise produced by the exhaust from the propulsive nozzle system of a jet engine.

The advent of aircraft of larger size and of higher speed capability has concomitantly resulted in an increase in the level of noise emitted therefrom. The increase in the level of noise has been primarily produced by the increase in thrust and in velocity of the hot gas streams discharged from the propulsive nozzle thereof. The level of noise so generated has reached a point which has caused increasing concern particularly in connection with low-altitude flight and in the vicinity of airports and brought on requirements for the reduction thereof.

It is a principal object of the present invention to provide means for reducing substantially the noise generated by the exhausts discharged at supersonic velocities from the propulsive nozzle system of a jet engine without the disadvantages of prior arrangements, particularly the long axial length of prior art systems.

It is another object of the present invention to provide noise suppression means for a supersonic jet engine which produces minimal degradation of thrust.

It is a further object of the present invention to provide noise suppression means for both subsonic and supersonic jet engines.

In accordance with an illustrative embodiment of the nozzle system of the present invention there is provided a duct which may be a propulsive nozzle. A plurality of hollow tubes each parallel to the axis of the duct and each having an inlet end and an outlet end are also provided mounted to a plate having major forces aligned generally perpendicular to the axis of the duct and having a plurality of apertures therein extending between the major faces. Each of the inlet ends of the tubes are sealed to the plate with the internal passageway of each tube registering with a respective aperture. Means are provided for coupling the flow of fluid from the duct to the inlet ends of the tubes. A plurality of conduits are further provided to form a plurality of passageways into which secondary flow is induced, the axis of each passageway parallel to the axis of the duct and each passageway larger in cross-sectional area than the cross section areas of a respective tube. The outlet end of each tube extends into the passageway of a respective conduit at the inlet end thereof.

The novel features which are believed to be characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which:

FIG. I shows in partial cross section a propulsive nozzle system in accordance with the present invention.

FIG. 2 is a sectional view of the apparatus of FIG. 1 taken along section lines 2-2 thereof.

Referring now to FIG. I, there is shown a duct 10, which may also be a propulsive nozzle or an orifice, having an inlet end Il suitable for connection to the output from ajet engine and having an outlet end 12 to which is connected apparatus which forms with the duct a nozzle system of reduced noise emission. The apparatus includes a plurality of secondary nozzles or tubes 13, each having a passageway I4 parallel to the axis of the duct and each having an inlet end and an outlet end 16. The tubes I3 are supported in a plate having a pair of major faces 21 and 22 aligned generally perpendicular to the axis 23 of the duct 10 and having a plurality of apertures 24 therein extending between the major faces. Each of the inlet ends I5 of the tubes 13 are sealed to the plate 20 with each passageway of the tube 13 registering with a respective aperture 24.

The apparatus also includes a multiple shroud assembly 29 comprising a plurality of conduits 30. each having a passageway parallel to the axis 23 of the duct I0 and each larger in cross-sectional area than the cross-sectional areas of a respective tube 13. Each conduit 30 has an inlet end 31 and an outlet end 32. The outlet end 16 of each tube extends into the passageway at the inlet end 3I of a respective conduit 30. Each of the conduits 30 has a cross section which is in the form of a hexagon having sides of equal length as can be seen more clearly from FIG. 2 which is a sectional view of the shroud assembly taken along section lines 22 of FIG. I showing the alignment of the tubes 13 in respect to the conduits 30. The shroud assembly 29 is supported by means of a flange 34 extending about the outer surface thereof and secured to a corresponding flange 17 on the duct 10 by means of a plurality of cross members 18.

The fluid flow from the outlet end I2 of the duct 10 to the inlets of the tubes 13 is provided by means of a contoured surface member 40. The contoured surface member is shown at the inlet end 41 thereof abutting the outlet end 12 of the duct 10 and at the outlet end 42 thereof abutting the plate 20 supporting the tubes 13. It will be understood that means are readily available in the art for providing a satisfactory seal at the inlet end and the outlet ends of the contoured surface member 40 to the duct 10 and to the plate 20, respectively, and form no part of the present invention. It will further be understood that the configuration shown and described in FIG. I is shown in the manner in which it would be used in reducing noise from the exhaust of a jet engine in low-altitude flight and in the vicinity of airports. Once the aircraft to which the apparatus including the tubes I3 and shrouds 30 is attached had reached a point sufficiently distant from places where the noise generated thereby would be objectionable, such apparatus would be detached from the duct, that is, the tubes 13 would be retracted and the shroud assembly 29 similarly would be retracted in conjunction tubes 13 or independent thereof. The contoured surface member 40 could be utilized to provide a convergent nozzle configuration to the nozzle 10 shown simply by providing means that are available in the art for forming from contoured surface member 40 a convergent nozzle. It will be understood that the contoured surface could also be made to form the divergent portion of a convergentdivergent propulsive nozzle. Also, it will be understood that the configuration shown in FIG. I could represent a nozzle system for ground transportation vehicles in which retraction of the apparatus which reduces the noise emission from the system would be unnecessary.

Each of the tubes 13 in the assembly shown has the same cross-sectional area and the tubes are regularly spaced in horizontal rows 50 and vertical columns 51 as indicated in FIG. 2 in which the center of a tube in one row forms with the centers of two adjacent tubes in an adjacent row the apices of an equilateral triangle. Such tubes are formed into a bundle of circular cross section. Such an arrangement enables the conduits 30 of the shroud assembly 29 to be in the form of equilateral hexagons in cross section. Each of the hexagons are of the same cross-sectional area. A side of one hexagon abuts the side of an adjacent hexagon. The aggregate cross-sectional area of the passageway of the tubes 13 is made equal to the cross-sectional area of the throat of the convergent nozzle formed by the duct 10 and the contoured surface 40 to provide adequate passageway for the flow of gases from the outlet end 12 of the duct 10 into the shroud assembly 29. The spacing between the plate 20 and the inlet ends 31 of the shrouds 30, or the effective length of the tubes 13 is made sufficient to enable adequate ambient air to flow into all of the inlet ends 31 of the shrouds 30 for achieving noise suppression in a manner to be described hereinafter. Advantageously the rear face of the plate 20 may be made conical to facilitate the flow of ambient air to the conduits 30 located in the inner portions of the assembly 29.

The number of tubes 13 utilized will depend upon the axial shortening of the length of the nozzle system desired for the particular application. With a large number of tubes 13 the axial length of the nozzle system can be limited to a small increase in axial extent over a nozzle without the apparatus producing sound suppression. For a smaller number of tubes, a larger axial length in the nozzle system would result as longer lengths of tubes and shrouds would be needed to achieve the same degree of sound suppression. Of course, with a smaller number of tubes, a smaller thrust loss would be incurred. The outlet ends 16 of each of the tubes 13 extends for a short distance, for example 1% times the diameter of the tube 13, into its respective shroud conduit 30 to minimize sound radiation and provide adequate aspiration of ambient air into the conduits 30.

The shroud assembly 29 is in the form of a honeycomb structure in which each of the conduits 30 of the hexagonal cross section are stacked to form a honeycombed array. The axial length of the shroud assembly 29 is made sufficiently long to provide, particularly for supersonic applications, adequate reduction in the velocity of the gases flowing therethrough as well as to provide uniformity in the velocity of exhaust from the outlet end of a conduit over a plane perpendicular to the longitudinal axis thereof. Good results are achieved in this respect with an axial length of conduit in excess of 20 times the diameter of a tube. For a length of conduit of 20 times the diameter of the conduit, the cross-sectional area of the conduit is made approximately 2.5 times the crosssectional area of a tube to provide good aspiration of ambient air induced by the flow of exhaust gases into the conduits 30.

The operation of the present invention will be understood by first considering the manner in which a shroud coacts with the exhaust from a nozzle to provide a reduction of noise emitted therefrom. In the case of the propulsive nozzles from which the exhausts flow at supersonic velocities, it has been found that exhaust gases travel at supersonic velocities for a considerable distance beyond the outlet end thereof, that is, many nozzle outlet diameters before a point is reached at which the velocity thereof is reduced to sonic velocities. The distance of such a point, referred to as the sonic point, from the outlet end of a nozzle is a function of the Mach number of the exhaust at the outlet end and is also a function of the diameter of the outlet end, that is, it varies directly as the diameter of the outlet end. Accordingly, it is apparent that for nozzles of small diameter the sonic point is close to the outlet end thereof. It has also been determined that the major source of noise in a jet exhaust is that portion of the jet exhaust between the outlet end and the sonic point. Accordingly, providing a primary or propulsive nozzle with a plurality of secondary nozzles each of small cross-sectional area reduces the overall distance of the sonic point from the outlet end of the primary nozzle and facilitates the action of shroud assemblies for shielding the source of noise. The shrouds 30 also provide a means for inducing flow of ambient air into the exhaust from the tubes 13 to reduce the velocity thereof. The shrouds 30 further enable mixing of exhaust gases with ambient air to take place to provide a uniform velocity profile at the outlet end thereof.

When tubes 13 of small diameter are used, the sonic point is quite close to the outlet end thereof. Accordingly, the shrouds 30 utilized can be quite short to provide the necessary shielding of the major source of generation of the noise. The shielding action can be aided by the attachment ofa sound-absorbing material such as porous asbestos or stainless steel wool to the forward inside surfaces of the shrouds 30. The shrouds 30 are made sufficiently large in cross section so that they act to induce adequate ambient air flow which reduces the velocity of the exhaust gases. Also, the shrouds 30 are made of sufficient length to provide substantially uniform discharge velocities over a cross-sectional area of the outlet end thereof.

The number of tubes utilized may vary from just a few, for example four in number, to over a hundred depending upon the requirements for the particular application. Where it is desired to reduce the overall axial length of the noise suppression apparatus considerably, a larger number of tubes would be used. Where such a requirement is not nearly as stringent, a smaller number of tubes may be utilized.

in connection with the removal of the noise suppression apparatus from the path of the exhaust of duct 10, the plate 20 could be segmented or sectored to facilitate the retraction thereof from the path of the exhaust. Also, while a configuration has been shown in which each of the tubes 13 are of the identical cross section and are arranged in regular order, and correspondingly shrouds 30 of the same cross section are regularly arranged, it will be appreciated that such an arrangement is not mandatory. The tubes 13 could be of different cross sections and accordingly the individual conduits or shrouds for each tube would be formed to provide the optimum shielding and aspirating action described above to effeet a reduction and a rendering uniform of the velocity of the exhaust gases from the outlet ends of the conduits.

It will be understood that the noise suppression apparatus shown described is equally effective for suppression of noise from propulsive nozzles which emit gases at subsonic as well as at supersonic velocities.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. In combination,

a nozzle assembly for a jet engine including a plurality of nozzles of small cross-sectional area, said nozzles being closely spaced and having axes substantially parallel,

each of said nozzles having an inlet end and an outlet end,

means for supplying said inlet ends from a common source,

a cylindrical shroud assembly including a plurality of shrouds of small cross-sectional area, said shrouds being closely spaced and having axes substantially parallel to the axes of said small nozzles, each of said shrouds having an inlet end and an outlet end, the inlet end of each of said shrouds positioned adjacent the outlet end of a respective nozzle to receive the fluid discharged therefrom,

the passageway of each shroud having a cross-sectional area substantially greater than the cross-sectional area of the outlet end of a corresponding nozzle whereby discharge of fluid from said nozzle into said shroud induces substantial ambient flow into said shroud, and the length of each of said shrouds in the axial direction being several times the diameter of a respective nozzle to provide thorough mixing of the flow from the outlet end of a corresponding nozzle with said ambient flow to reduce substantially the velocity of the flow emerging at the outlet end thereof and to produce substantially uniform velocity in flow at the outlet end thereof.

2. A nozzle system for ajet engine comprising,

a duct having an outlet end,

a plurality of tubes, each tube providing a passageway parallel to the axis of said duct and having an inlet and an outlet end, the cross-sectional area of each of said tubes being substantially smaller than the cross-sectional area of said duct,

means for coupling the exhaust from said duct to the inlet ends of said tubes,

a plurality of cylindrical conduits, each conduit providing a cylindrical passageway having its longitudinal axis parallel to the axis of said duct and each conduit substantially larger in cross-sectional area than the cross-sectional area of a respective tube, each conduit having an inlet and an outlet end, the outlet end of each tube extending a short distance into the inlet end of a respective conduit to induce ambient flow therein, the length of each of said conduits in the axial direction being several times the diameter of a respective tube to provide thorough mixing of the flow from the outlet end of a corresponding tube with said ambient flow to reduce substantially the velocity of the flow emerging at the outlet end thereof and to produce substantially uniform velocity in flow at the outlet end thereof.

3. The combination of claim 2 in which said tubes have passageways which are circular in cross section and of the same cross-sectional area in which said tubes are arranged in horizontal rows and vertical columns, the center of a cross section of a tube in one row forming with the centers of the cross sections of adjacent tubes in an adjacent row the apices of an equilateral triangle, and in which the cross section of the 

1. In combination, a nozzle assembly for a jet engine including a plurality of nozzles of small cross-sectional area, said nozzles being closely spaced and having axes substantially parallel, each of said nozzles having an inlet end and an outlet end, means for supplying said inlet ends from a common source, a cylindrical shroud assembly including a plurality of shrouds of small cross-sectional area, said shrouds being closely spaced and having axes substantially parallel to the axes of said small nozzles, each Of said shrouds having an inlet end and an outlet end, the inlet end of each of said shrouds positioned adjacent the outlet end of a respective nozzle to receive the fluid discharged therefrom, the passageway of each shroud having a cross-sectional area substantially greater than the cross-sectional area of the outlet end of a corresponding nozzle whereby discharge of fluid from said nozzle into said shroud induces substantial ambient flow into said shroud, and the length of each of said shrouds in the axial direction being several times the diameter of a respective nozzle to provide thorough mixing of the flow from the outlet end of a corresponding nozzle with said ambient flow to reduce substantially the velocity of the flow emerging at the outlet end thereof and to produce substantially uniform velocity in flow at the outlet end thereof.
 2. A nozzle system for a jet engine comprising, a duct having an outlet end, a plurality of tubes, each tube providing a passageway parallel to the axis of said duct and having an inlet and an outlet end, the cross-sectional area of each of said tubes being substantially smaller than the cross-sectional area of said duct, means for coupling the exhaust from said duct to the inlet ends of said tubes, a plurality of cylindrical conduits, each conduit providing a cylindrical passageway having its longitudinal axis parallel to the axis of said duct and each conduit substantially larger in cross-sectional area than the cross-sectional area of a respective tube, each conduit having an inlet and an outlet end, the outlet end of each tube extending a short distance into the inlet end of a respective conduit to induce ambient flow therein, the length of each of said conduits in the axial direction being several times the diameter of a respective tube to provide thorough mixing of the flow from the outlet end of a corresponding tube with said ambient flow to reduce substantially the velocity of the flow emerging at the outlet end thereof and to produce substantially uniform velocity in flow at the outlet end thereof.
 3. The combination of claim 2 in which said tubes have passageways which are circular in cross section and of the same cross-sectional area in which said tubes are arranged in horizontal rows and vertical columns, the center of a cross section of a tube in one row forming with the centers of the cross sections of adjacent tubes in an adjacent row the apices of an equilateral triangle, and in which the cross section of the passageway of each of said conduits is a first equilateral hexagon of predetermined cross section and in which the periphery of the cross section of each of said conduits is a second equilateral hexagon, said conduits being arranged in horizontal rows and vertical columns, the center of said second hexagon in one row forming with the centers of adjacent second hexagons in an adjacent row the apices of an equilateral triangle, a side of each of said second equilateral hexagons abutting a side of an adjacent second equilateral hexagon. 